Diesel engines include fuel injection valves for high injecting high-pressure fuel into combustion chambers.
FIG. 6 depicts one type of fuel injection valve “A,” as disclosed in JP2003-148277A (hereinafter referred to as “Reference 1”). The fuel injection valve “A” includes a nozzle portion 120, a backpressure chamber 130, a valve chamber 140, a control valve 170, and an actuator 180. The nozzle portion 120 includes an injector 110 and a nozzle needle 100. The nozzle needle 100 is operable to open and close the injector 110. The backpressure chamber 130 is adapted to accumulate high-pressure fuel, which urges the nozzle needle 100 in a nozzle-closing direction toward the injector 110. The valve chamber 140 communicates with the backpressure chamber 130, a low-pressure conduit 150, and a high-pressure conduit 160. The control valve 170 is installed in the valve chamber 140 and is operable to selectively interrupt communication between the valve chamber 140 and the low-pressure and high-pressure conduits 150, 160. The actuator 180 is operable to drive the control valve 170.
The actuator 180 includes a piezoelectric actuator 180. The piezoelectric actuator 180 includes a plurality of laminated piezoelectric devices that extend or retract in response to a charging voltage. The extension or retraction of the piezoelectric devices is transmitted to the control valve 170 via a first piston 200 disposed in an oil-tight chamber 190 and a second piston 210.
The valve chamber 140 containing the control valve 170 includes a low-pressure port 220 and a high-pressure port 230. The low-pressure port 220 communicates with the low-pressure conduit 150. The high-pressure port 230 communicates with the high-pressure conduit 160. The control valve 170 is operable to close one of the low-pressure port 220 and the high-pressure port 230.
When the control valve 170 closes the high-pressure port 230, it opens the low-pressure port 220. When the low-pressure port 220 opens, the backpressure chamber 130 freely communicates with the low-pressure conduit 150 via the valve chamber 140. This decreases the fuel pressure in the backpressure chamber 130 allowing the nozzle needle 100 to move toward the backpressure chamber 130 away from the injector 110 and, thus, allowing fuel to travel through the injector 110 from the high-pressure conduit 160. Alternatively, if the control valve 170 closes the low-pressure port 220, the communication between the backpressure chamber 130 and the low-pressure conduit 150 terminates. The fuel pressure in the backpressure chamber 130 increases and the nozzle needle 100 moves in the valve-closing direction to close the injector 110.
Accordingly, to open the low-pressure port 220 and close the high-pressure port 230, the actuator 180 must force the control valve 170 downward against the strength of the high-pressure fuel contained in the valve chamber 140. The piezoelectric actuator 180 requires a high charging voltage to achieve this, as indicated by the dashed line in FIG. 3. With continued reference to FIG. 3, the shaded circle indicates the load required for the piezoelectric actuator 180 to move the control valve 170 to open the low-pressure port 220. The shaded square indicates the load required for the piezoelectric actuator 180 to move the control valve 170 to close the high-pressure port 230. Thus, it should be understood that the fuel injection valve “A” requires a larger output strength and displacement to close the high-pressure port 230 than to simply open the low-pressure port 220.
FIG. 7 depicts a fuel injection valve “B” as disclosed in Japanese Patent Application No. 2002-345588, hereinafter referred to as “Reference 2.” It is important to note that fuel injection valve “B” was disclosed in JP2004-176656A on Jun. 24, 2004, which is subsequent to the filing date of Japanese Patent Application No. 2003-379566, to which this application is based upon and claims the benefit of priority. Fuel injection valve “B” is similar to the fuel injection valve “A” described above with the exception that the control valve 170 is equipped with a pressure-balancing valve comprising a guide portion 240 disposed in a guide hole 250. The guide portion 240 operates to cancel the high-pressure of the fuel acting on the control valve 170 while the control valve 170 opens the low-pressure port 220 and closes the high-pressure port 230.
The guide portion 240 is connected to and moves with the control valve 170. The fuel pressure acting on the guide portion 240 urges the control valve 170 downward. This balances the fuel pressure urging on the control valve 170 upward. Therefore, the fuel injection valve “B” requires less strength to close the high-pressure port 230.
The guide portion 240 is installed for sliding displacement in the guide hole 250. The guide hole 250 fluidly communicates with the low-pressure conduit 150 via a connecting conduit 260 such that a low-pressure acts on the bottom of the guide portion 240. This low-pressure reduces the strength required to open the low-pressure port 220 to a value that is smaller than that required of the fuel injection valve “A” disclosed in Reference 1. FIG. 3 depicts the load required to open the low-pressure port 220 (identified by the empty circle), the load required to close the high-pressure port 230 (identified by the empty square), and the charging voltage required by the piezoelectric actuator 180 of the fuel injection valve “B” (identified by the solid line).
However, the fuel injection valve “B” disclosed in Reference 2 includes some potential for operating deficiencies. As stated above, the lower end of the guide hole 250 is connected to the low-pressure conduit 150 via the connecting conduit 260. This creates a difference in fuel pressure between the top and bottom sides of the guide portion 240. This difference in fuel pressure can cause fuel leakage through any clearance provided between the guide portion 240 and the guide hole 250.
Furthermore, it should be noted that the guide portion 240 axially and radially supports the control valve 170. The guide hole 250 maintains the radial disposition of the control valve 170 by slidably supporting the guide portion 240. Therefore, if the valve seat of the low-pressure port 220 is conically shaped, any error in the coaxial alignment between the low-pressure port 220 and the guide hole 250 will increase uneven wearing of the guide portion 240 and/or the guide hole 250, thereby increasing the fuel leakage described above. Alternatively, if the valve seat of the low-pressure port 220 includes a flat surface, any error in the angle of the flat surface relative to the axis of the guide hole 250 will decrease the seating quality of the control valve 170 against the low-pressure port 220.